Temperature-drop stress overlooked up to now in horticultural crop production - Importance of the leaf injury and the clarification of its mechanism

(1)15种苦艾科植物中有3种对降温冲击敏感。(2)当降温速率达到3℃/s或更高时，叶片发生伤害。快速降温引起的表皮收缩被认为是外界的刺激。(3)对植物体内的伤害处理，包括切除叶片或枝条，在远离伤口的部位造成类似于叶片温降休克的伤害。推测伤害处理和叶温下降冲击引起的反应与引发伤害的反应相同。(4)温度、光照强度和相对湿度等环境因子影响伤害处理引起的细胞死亡。认为高敏感状态是由创伤和降温引起的，从而提高了全身对外界刺激的敏感性。(5)在干旱和高温条件下，水分胁迫更容易诱发高敏感状态。(6)高敏感状态的诱导存在着日变化。诱导水平上午低，下午上升，夜间不诱导。在此基础上，建议根据需要在上午进行顶灌。

(1) Three species of the Acanthaceae of 15 species of the Gesneriaceae were found as a sensitive plant to the temperature drop shock in this study.(2) The leaf injury occurred when the temperature dropped at the speed of 3℃/second or more. The shrinkage of epidermis caused by the rapid temperature drop was thought to be perceived as the external stimulus.(3) Wounding treatment to the plant body including the excision of a leaf or a shoot caused the injury similar to the leaf temperature drop shock at sites distant from the wound. It was guessed that wounding treatment and the leaf temperature drop shock caused the same reaction as a trigger of the injury.(4) Environmental factors such as temperature, light intensity and relative humidity affected the cell death caused by wounding treatment. Hypersensitive state was thought to be induced by the wound and the temperature drop to improve be sensitivity of the whole body to the external stimuli afterwards.(5) Hypersensitive state tended to be induced much more by water stress under the dry condition and the high temperature.(6) There was a diurnal change in the inducement of the hypersensitive state. The level of the inducement was low in the morning, rose in the afternoon, and was not induced at night. Then, it was suggested that overhead irrigation was recommended to conduct in the morning when needed.